Nerve growth is promoted by a wide range of molecules, including the cell surface adhesion molecules (CAMs) NCAM and N-cadherin. In particular, N-cadherin is the predominant mediator of calcium-dependent adhesion in the nervous system. N-cadherin is a member of the classical cadherin family of calcium-dependent CAMs (Munro et al., In: Cell Adhesion and Invasion in Cancer Metastasis, P. Brodt, ed., pp. 17-34, R G Landes Co.(Austin Tex., 1996). The classical cadherins (abbreviated CADs) are integral membrane glycoproteins that generally promote cell adhesion through homophilic interactions (a CAD on the surface of one cell binds to an identical CAD on the surface of another cell), although CADs also appear to be capable of forming heterotypic complexes with one another under certain circumstances and with lower affinity. Cadherins have been shown to regulate epithelial, endothelial, neural and cancer cell adhesion, with different CADs expressed on different cell types. N (neural)--cadherin is predominantly expressed by neural cells, endothelial cells and a variety of cancer cell types. A detailed discussion of the classical cadherins is provided in Munro SB et al., 1996, In: Cell Adhesion and Invasion in Cancer Metastasis, P. Brodt, ed., pp.17-34 (R G Landes Company, Austin Tex.).
The structures of the CADs are generally similar. As illustrated in FIG. 1, CADs are composed of five extracellular domains (EC1-EC5), a single hydrophobic domain (TM) that transverses the plasma membrane (PM), and two cytoplasmic domains (CP1 and CP2). The calcium binding motifs DXNDN (SEQ ID NO:8), DXD and LDRE (SEQ ID NO:9) are interspersed throughout the extracellular domains. The first extracellular domain (EC1) contains the classical cadherin cell adhesion recognition (CAR) sequence, HAV (His-Ala-Val), along with flanking sequences on either side of the CAR sequence that may play a role in conferring specificity. Synthetic peptides containing the CAR sequence and antibodies directed against the CAR sequence have been shown to inhibit CAD-dependent processes (Munro et al., supra, Blaschuk et al., J. Mol. Biol. 211:679-82, 1990; Blaschuk et al., Develop. Biol. 139:227-29, 1990; Alexander et al., J. Cell. Physiol. 156:610-18, 1993). The three-dimensional solution and crystal structures of the EC1 domain have been determined (Overduin et al., Science 267:386-389, 1995; Shapiro et al., Nature 374:327-337, 1995).
N-cadherin is known to promote neurite outgrowth via a homophilic binding mechanism. N-cadherin is normally found on both the advancing growth cone and on cellular substrates, and the inhibition of N-cadherin function results in diminished neurite outgrowth. Such inhibition may be the result of pathology or injury involving severed neuronal connections and/or spinal cord damage. In such cases, enhancement of N-cadherin mediated neurite outgrowth would be beneficial. However, previous attempts to promote neurite outgrowth have achieved limited success due, in part, to difficulties associated with maintaining continuous growth over a particular defined region.
Accordingly, there is a need in the art for compounds that modulate and/or direct neurite outgrowth without such disadvantages. The present invention fulfills this need and further provides other related advantages.